Vehicle interior panels typically include a decorative aspect, providing the passenger cabin of a vehicle with a desired aesthetic. Combinations of different types of materials, textures, shapes, tactile features, and visual features can be used with such panels to provide the passenger cabin with any of a variety of different ambiences, from luxurious to utilitarian. Modern polymer-based materials can be shaped into complex contoured shapes and are used extensively in vehicle interiors due to the available design freedom. Over time, polymer-based material have become commonplace in vehicle interiors, prompting some vehicle manufacturers to seek to differentiate from the commonplace interiors by including different non-polymeric materials, such as leather, fabric, metal, etc. as interior design elements. But the ease of shaping polymer-based materials is lost when these other material types are employed, forcing interior designers to compromise and forego desired shapes and surface contours when non-polymeric materials are desired.
U.S. Patent Application Publication No. 2013/0221698 by Nowik et al. discloses examples of a negative thermoforming process useful to create sharp design features in the decorative surface of interior vehicle covering materials. The process relies on a polymer-based sheet of material that is heated before the intended show surface of the material is pressed against a tool surface. The process is an improvement over positive thermoforming processes in which the back or underside of the sheet is pressed against a tool surface because sharper features can be formed directly into the show surface than through the thickness of the material, particularly when the thickness of the sheet material is relatively high.